Sizing Domestic Water Pipes

For long runs and tall houses remember to use larger supply pipes

Some plumbers successfully size
residential supply pipes based
on long experience or rules of
thumb. But in unusual circumstances
— when a house has low
pressure, long pipe runs, an extensive
irrigation system, or a large whirlpool
tub — rules of thumb may result in
undersized pipes that perform poorly
or don’t meet code (see Figure 1, next
page).
To accurately size residential water
supply pipes, you need to have information
on six important variables:
• code requirements
• available minimum static pressure at
the water meter or pressure tank
• the pressure-reducing effect of any
water meter, backflow preventer,
water softener, and/or whole-house
filter
• length of pipe to the most remote
fixture in the building
• height of the building
• water